Abstract Low levels of bisphenol A (BPA;2,2-bis(4-hydroxyphenyl)propane) are detectable throughout the US population. Whether these low levels of exposure pose a human health risk remain controversial and uncertain. Comparable low levels of BPA cause behavioral abnormalities in adult rodents exposed during critical periods of central nervous system (CNS) development, leading the National Toxicology Program to recently report concern that low dose BPA exposure can impair CNS development. The predominant assumption that BPA exerts its CNS effects through estrogen receptor (ER) activation is unlikely due to BPA's weak binding affinity for classical ERs. However, BPA exhibits 100- to 10,000-fold greater binding affinity for estrogen related receptor gamma (ERR3). ERR3 is a nuclear receptor that is highly expressed in the brain and placenta during critical periods of development, has no known endogenous ligand, and is constitutively active at estrogen response elements (EREs). This proposal will test the hypothesis that low dose developmental BPA exposure perturbs CNS development and behavior by maintaining ERR3 constitutive activity during critical windows of development resulting in abnormal expression of genes containing EREs or ERREs. Preliminary studies conducted to support this two year exploratory grant suggest that developmental exposure to non-teratogenic, low concentrations (<1<M) of BPA increases motor activity in larval and adult zebrafish. Two specific aims have been developed to define the role of ERR3 in mediating the physical and behavioral effects of low dose BPA. In the first Specific Aim, we will determine whether environmentally relevant concentrations of BPA affect nervous system development and functions in zebrafish developmentally exposed to low concentrations of BPA. The role of ERR3 in producing these responses will be determined by repressing ERR3 expression specifically during the BPA exposure window. In the second Specific Aim, comparative gene expression studies will be used to identify in vivo functional biomarkers and determine the role of ERR3 in their expression. We will also utilize a powerful, newly described transgenic methylation-responsive fish to investigate epigenetic effects of BPA exposure specifically in the brain. These experiments will probe for the first time a potential epigenetic mechanism by which low concentration BPA exposure impairs CNS function, and define the role of ERR3 in mediating these effects. The role of ERR3 in mediating low dose BPA effects on the CNS has not been previously investigated. The zebrafish model is ideally suited to quickly and definitively answer whether ERR3 is central to the mechanism of BPA's action on the developing CNS. This proposal will benefit the scientific community, industry, and the public by defining whether the most likely candidate receptor, ERR3, mediates BPA's low dose effects on CNS development and behavior. PUBLIC HEALTH RELEVANCE: In recent years the public and the scientific community have become concerned with the risk that bisphenol A (BPA) may pose to human health. This project will use the unique advantages of the embryonic zebrafish model to dissect the mechanism by which low concentrations of BPA interact with and perturb central nervous development and function.